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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
      window.onload = function(){
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               // console.log(radius);
        input_element[3].onclick=function(){
            var radius = input_element[0].value;
            var radius1 = input_element[1].value;
            input_element[2].value = parseInt(radius)+parseInt(radius1);
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            input_element[1].value = "";
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</head>
<body>
        <form action="">
        数值<input type="text" name="" id="" placeholder="请输入第一个数"><br>
        数值<input type="text" name="" id="" placeholder="请输入第而个数"><br>
        结果<input type="text" name="" id=""><br>
        <input type="button" value="加">
        <input type="button" value="减">
        <input type="button" value="乘">
        <input type="button" value="除">
        <input type="button" value="重置">
    </form>
</body>
</html>